1. Field of the Invention
The present invention relates to a semiconductor device which comprises at least one pair, i.e., one or more pairs of transistors and resistors, and more particularly, to prevention countermeasures against unevenness of circuit operations due to differences between characteristics and resistance values of transistors.
2. Description of the Background Art
FIG. 6 is a circuitry diagram showing one example of a muting circuit for general audio signals. The circuit comprises resistors R1 through R8, transistors Q1 and Q2 and circuit boards P1 and P2.
As shown in FIG. 6, as a control signal turns on the pair of muting transistors Q1, Q2, a pair of audio signals, one for the right-hand side and the other for the left-hand side, are muted.
While it is a requirement for a pair of speakers, one for the right-hand side and the other for the left-hand side to have equivalent muting characteristics to each other in the muting circuit for audio signals as described above, the two transistors Q1, Q2 incorporating resistors are customarily fabricated separately from each other and individually mounted to the circuit boards P1, P2, respectively.
By the way, in order to mute a pair of the left and the right audio signals by approximately equal attenuation amounts at the same time, characteristics of the transistors Q1, Q2 must match to each other and resistance values of the resistor elements R7, R8 must be approximately equivalent to each other.
However, it is not easy to ensure that the transistors Q1, Q2 which are manufactured separately from each other respectively for the circuit boards P1, P2 have matching characteristics to each other.
Further, it is not easy, either, to ensure that the resistor elements R7, R8 which are disposed separately from each other on an insulation film which covers a surface of semiconductor elements have matching resistance values to each other. To do so leads to an increase in a manufacturing cost, and in addition, to equalize characteristics to a sufficient extent is difficult.
Still further, where two discrete semiconductor elements are used as customarily practiced, since this is an increased number of components, a substrate mounting area and a mounting cost increase.
Accordingly, an objective of the present invention is to provide for a semiconductor device which allows a decrease in a cost, a reduction of a substrate mounting area and equalization of characteristics of a pair of transistors and the like.
A semiconductor device according to the present invention comprises: a semiconductor substrate of one conductivity type; a separation strip of the one conductivity type which splits the semiconductor substrate into pairing regions and surrounds the semiconductor substrate, the separation strip having a high impurity concentration than a front surface side of the semiconductor substrate; a pair of vertical type semiconductor elements which share the semiconductor substrate as a collector region, the semiconductor elements comprising base regions of a reverse conductivity type which are formed respectively in the pairing regions and emitter regions of the one conductivity type which are formed within the base regions of the reverse conductivity type; an insulation film which covers a surface of the semiconductor substrate; and at least a pair of resistor elements formed in the pairing regions on the insulation film
In the semiconductor device according to the present invention, the two vertical type semiconductor elements are formed in a portion of the semiconductor substrate and electrically separated from each other by the separation strip, the insulation film covers the surface of the semiconductor substrate, and the resistor elements are formed on the insulation film. Hence, one semiconductor chip realizes the two semiconductor elements which are electrically separated from each other and which have equivalent characteristics to each other and the plurality of resistor elements. Further, since the semiconductor substrate is shared as the collector region unlike in a conventional semiconductor device, it is possible to reduce a cost and a size.
In addition, in the semiconductor device above, the diffusion depth and the impurity concentration of the separation strip are equivalent to or larger than those of the emitter regions.
Since this realizes a structure in which it is possible to form the semiconductor region of the separation strip utilizing a step of forming a diffusion region of a transistor, a manufacturing cost of the semiconductor device is reduced. Further, since the separation strip is not formed by combination of semiconductor regions of two conductivity types of the P type and the N type but by semiconductor regions of one conductivity type, the separation strip demands a smaller area, which in turn reduces an area needed for the entire semiconductor device and a manufacturing cost. Still further, since the concentration and the depth of the separation strip are equivalent to those of the emitter regions and the separation strip has the same conductivity type as the semiconductor substrate but a higher impurity concentration than the semiconductor substrate, it is possible to prevent mutual interference between the vertical type semiconductor elements at the surface side of the semiconductor elements on the surface of the semiconductor substrate.
Moreover, in the semiconductor device above, an outer periphery of the separation strip is in contact with a scribe line of the reverse conductivity type which surrounds the semiconductor substrate, and a region which corresponds to the scribe line is not formed at a position of a common region of the separation strip at which the vertical type semiconductor elements are opposed with each other through the separation strip.
The reason a lower portion of the common region of the separation strip does not comprise the reverse conductivity type region which exists in the scribe line is to prevent the common region of the separation strip from disconnecting this element which is usually fabricated separately from each other and to decrease the area which the separation strip occupies in the semiconductor substrate so that a compact size is realized.
Further, in the semiconductor device above, a bonding pad which is connected to the emitter regions and the base regions is disposed on the outer periphery side of the separation strip to the common region of the separation strip.
This allows to shorten a wire, for example, which connects to the bonding pad.
Further, in the semiconductor device above, the vertical type semiconductor elements are opposed with each other through the separation strip, and a common wire for connecting the resistor elements to the emitter regions or the base regions is disposed in the vicinity of the common region of the separation strip.
This permits to effectively utilize a space which is created between the separation strip and the bonding pad disposed to the emitter regions and the base regions for the purpose of disposing the common wire, and makes it easy to ensure sufficient lengths of the resistor elements.
Further, in the semiconductor device above, a pair of resistor elements extending in equivalent directions is disposed in the same pairing regions with the pair of vertical type semiconductor elements.
Further, the vertical type semiconductor elements are opposed with each other through the separation strip and symmetric with respect to the common region of the separation strip.
Further, leads which are electrically connected to emitter electrodes and base electrodes of the vertical type semiconductor elements are disposed opposed against each other in both side portions of a mounting portion of a lead which seats the semiconductor substrate.
This makes it possible to shorten the wiring length of the wire which connects the lead and the electrodes.